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Optical Identification and Spectroscopy of the X-ray Transient MAXI J0556-332

ATel #3104; J. P. Halpern, Columbia U.
on 12 Jan 2011; 07:23 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Jules Halpern (jules@astro.columbia.edu)

Subjects: Optical, X-ray, Transient

Referred to by ATel #: 3110, 3112, 3116, 3119, 3327, 3349, 4524

Using the Hiltner 2.4.m telescope of the MDM Observatory and the wide-field imager/spectrograph OSMOS, I observed the optical counterpart of MAXI J0556-332 (Matsumura et al., ATel #3102) as localized by the Swift XRT (Kennea et al., ATel #3103). The star suggested by Kennea et al. at (J2000.0) R.A. = 05h56m46.28s, Decl. = -33d10'26.3" has brightened to R ~ 17.8 from its USNO B1.0 magnitude of R = 19.9. A spectrum covering the wavelength range 3970-6880 Angstroms obtained on 2011 January 12 05:50 UT reveals emission lines of H-alpha 6563 (EW = -16 A), He I 5876, He I 6678, and He II 4686 (EW = -4 A) at zero redshift. The He II line is stronger than H-beta. The H-alpha line has a broad base with FWZI = 3800 km/s.